Commentary: Is Polyethylene Glycol Toxicity From Intravenous Methocarbamol Fact or Fiction?

Methocarbamol is an antispasmodic muscle relaxant and was the fourth most-prescribed muscle relaxant by volume in the United States in 2021. Intravenous (IV) methocarbamol contains the excipient, polyethylene glycol (PEG), which has been implicated in metabolic acidosis and nephrotoxicity. Intravenous methocarbamol was first approved by the US Food and Drug Administration in 1959 and at that time the IV methocarbamol prescribing information warned of PEG-associated adverse drug events in patients living with renal impairment; however, the manufacturer acknowledged data were lacking to objectively support this claim. Clinicians prescribing and dispensing IV methocarbamol may encounter the warning for PEG-associated metabolic acidosis and nephrotoxicity without knowing the potential risks, or lack thereof, supporting or disavowing this phenomenon. This commentary debates the merits supporting and arguments refuting PEG-associated metabolic acidosis and nephrotoxicity in patients treated with IV methocarbamol.